1. Field of the Invention
The present invention is generally related to the field of knee prosthetics and specifically related to the field of tibial trays capable of providing high knee flexion with and without retention of the posterior cruciate ligament.
2. Description of Related Art
In U.S. Pat. No. 5,964,808 (the '808 patent) and U.S. Pat. No. 6,013,103 (the '103 patent) which are hereby incorporated herein by reference in their entirety, the assignee of the present patent application (Wright Medical Technology, Inc., of Arlington, Tenn.) introduced a knee prosthetic capable of better imitating the complex biomechanics and kinematics of the normal human knee. The knee prosthetic described in the '808 and '103 patents has been, and continues to be, successful, especially at facilitating movement within the normal ranges of knee flexion.
Various scientific publications recognize that the kinematics of a normal, uninjured knee when subject to deep or high knee flexion can become very complex. See, e.g., Bellemans, et al., Fluoroscopic Analysis of the Kinematics of Deep Flexion in Total Knee Arthroscopy, J. Bone Joint Surgery [Br] 84-B:50–3 (2002). Deep knee flexion, as used herein and in the prior art, is the same as high knee flexion and refers to relative movement of the femur with respect to the tibia to an angle of about 90° or greater. Such complex knee kinematics can be difficult to replicate using conventional knee prosthetics which are primarily intended to address more normal ranges of knee flexion.
Another issue associated with the implantation of knee prosthetics is that in some instances a surgeon may elect to retain the posterior cruciate ligament (PCL) of the knee when implanting tibial and femoral components of the knee prosthesis. Generally, it is believed by some that sparing the PCL facilitates a return to normal knee kinematics. Several publications have examined the effects of such PCL-sparing surgeries on knee kinematics, and in particular, the effects of PCL-sparing on knee kinematics in deep or high flexion. See, e.g., Most, et al., Femoral Rollback After Cruciate-Retaining and Stabilizing Total Knee Arthroplasty, Clinical Ortho. & Related Research, No. 410, pp 101–113 (2003); Bertin, et al., In vivo Determination of Posterior Femoral Rollback for Subjects Having a NexGen Posterior Cruciate-Retaining Total Knee Arthroplasty, 17 J. of Arthroplasty 1040–1048 (2002); Guoan et al., Cruciate-Retaining and Cruciate-Substituting Total Knee Arthroplasty, 16 J. of Arthroplasty 150–156 (Supp. 2001); Sorger, et al., The Posterior Cruciate Ligament in Total Knee Arthroplasty, 12 J. of Arthroplasty 869–879 (1997); Stiehl, et al., Fluoroscopic Analysis of Kinematics After Posterior Cruciate-Retaining Knee Arthroplasty, J. Bone Joint Surgery [Br] 77-B: 884–889 (1995); Mahoney, et al., Posterior Cruciate Function Following Total Knee Arthroplasty, 9 J. of Arthroplasty 569–578 (1994). Regardless of the efficacy of sparing the PCL, its retention often increases the complexity of knee kinematics throughout the range of knee flexion. In particular, PCL retention can result in combined shifting and pivoting of the femur with respect to the tibia due to its exertion of a laterally directed force on the femur.
Different prosthetic devices have been developed to address the various issues associated with deep knee flexion. In one example, there are knee prosthetics in which the tibial tray rotates with respect to the tibia, by being mounted for rotation on its tibial base. In another example, there are knee prosthetics in which the tibial tray translates (or slides) with respect to the tibia, by being mounted for translation (sliding) on its tibial base. There are also knee prosthetics in which the tibial tray both rotates and translates with respect to the tibia, by being mounted for rotation and translation on its tibial base. Although these prosthetic devices provide one option to facilitate high knee flexion, they are relatively complex due to the required relative movement of the components with respect to their supporting bones.
Prosthetic devices have also been developed having a high anterior lip that allows for resection of the PCL, or protects the PCL in a PCL-sparing surgery. However, additional options for PCL sparing, especially prosthetics that also account for deep knee flexion, are still desirable.
Therefore, it would be advantageous to have a knee prosthesis that allows for more normal kinematic motion at higher or deeper flexion angles. In addition, it would be advantageous if such a prosthetic provided for retention of the PCL as is preferred by many surgeons.